1. Field of the Invention
The present invention relates to a reading unit detachably mountable on a recording apparatus, and a recording apparatus capable of mounting such reading unit on it.
2. Related Background Art
As a reading unit detachably mountable on a printing apparatus, there are conventionally a serial reading unit of the type that can be exchanged with a recording head mounted on the carriage of a printing apparatus, and a line reading unit that can be detachably mounted.
For the serial reading unit exchangeable with the recording head, no shutter mechanism is provided to protect the lens front of the optical reading system. Also, for the system that detachably mounts the line reading unit, no shutter of closing and opening type is provided to protect the lens and the light source, but a transparent plate or the like is arranged in front of the lens and the light source instead of the shutter.
The conventional detachable reading unit described above may often be located in a position other than the one regularly arranged for mounting because the unit should be made detachable. In this case, the front part of the lens is liable to collide with some other parts unexpectedly because no shutter mechanism is provided to protect the lens front. As a result, the image signals may sometimes become inaccurate for reading.
Also, for the detachable line reading unit having the transparent plate arranged to protect the lens and the light source, the transparent protection plate itself is damaged in some cases. If the palate is damaged, the image signals become inaccurate as in the case described above.
Further, in any one of the cases described above, the image signals may sometimes become inaccurate due to dust or other particles adhering to the lens or the transparent plate.
Also, an image reading device serving as a reading unit is generally provided with a plurality of light emitting elements and photodetecting elements. The light emitted from the light emitting elements illuminates the surface of a source document through light emitting fibers or the like, and then, the reflected light from the source document are received by the photodetecting elements through the light detecting fibers or the like, thus reading the source document.
Then, a control is arranged to determine the density of a source document, the so-called gradation, depending on the intensities of the light received by the photodetecting elements. Also, there is a method called binary control, which decides just on whether the representation is in black or in white without discriminating them finely in accordance with the densities.
As described above, it is necessary to determine the white portion on a source document as white and the black portion as black in accordance with the intensity of light received by the photodetecting elements, but there are some cases where the intensity of received light varies due to the variation or other causes that may exist among pluralities of light emitting elements and photodetecting elements to be used. If the intensity of received light should change, there is a possibility that white is read as black, and black as white. Then the contents that have been read are not the same as those of the source document.
Therefore, it is generally practiced that the white reference, called a white standard, whose reflective density is predetermined, is read in order to perform reading at a constant level at all times even if there are variations among the light emitting and photodetecting elements to be used, and that correction is made by the application of the white standard, thus enabling the intensity of the received light of the photodetecting elements to be recognizable as equal to that of the white standard.
Meanwhile, as recording methods adopted by recording apparatuses, there are, among others, ink jet method and wire-dot method, besides the thermal transfer method. Here, the ink jet method is such that recording is made by the recording head that does not touch the recording medium. With this method, a high speed recording is possible in high precision at lower noises. Therefore, the ink jet method is more in demand rapidly in recent years.
The ink jet recording method is structured to discharge ink droplets from the nozzles of the recording head for recording, and when the recording is at rest, the cap, which will be described later, is closely in contact with the surface of the recording head in order to prevent the nozzle unit of the recording head from being dried.
The recording head and the recording medium are arranged with a specific gap. At the time of recording, the ink droplets discharged from the nozzles of the recording head are caused to fly in the air in such specific gap. Images are formed when such ink droplets arrive at the recording medium.
Also, even at the time of recording, if a specific period of time elapses, while waiting for the data to be received, so that there is no discharge even after such period of time, the recording head is driven to move to the capping position. Then, predischarge is executed to prevent the nozzles of the recording head from being dried by discharging ink droplets into the cap. In this case, should the cap abut upon the recording head, the position of the recording head varies. This variation may disturb images when the next recording is performed. Therefore, the cap is arranged at a location away from the recording head at a certain distance. The predischarge is conducted toward the inside of the cap under such circumstance. As a result, the ink droplets fly in the air in this case, too, as at the time of recording.
It is ideal to discharge each of the ink droplets from the recording head in one mass. Actually, however, the discharged ink droplet may often be divided into one main droplet for the formation of an image on a recording medium, and a plurality of small ink droplets called ink mist, which is not related to the formation of any images.
The flying direction of the mist described above does not necessarily agree with that of the main droplet. Also, if the ink droplet is extremely small, the mist is caused to float in the recording apparatus to adhere to various parts in the interior of the apparatus.
Also, there are some cases where a main droplet is caused to bounce up the moment it arrives at a recording medium or the cap described earlier, and becomes floating mist, too.
Therefore, when an image reading device is integrally arranged on a carriage as described above, the reading unit of such image reading device is contaminated by the aforesaid mist, making it impossible to carry on image reading accurately.